High-range resolution radar real-time display apparatus

ABSTRACT

A high-range resolution radar display apparatus for generating a composite coarse and fine real-time radar display simultaneously without an intermediate storage system. One display comprises an extended length display which allows an operator to search an extended delta range and is generated by peak detecting range information from narrow bandwidth IF filters. The other display is a limited extent display featuring the maximum resolution capability of the correlation radar system for detailed target examination and is generated by feeding the information from each of the IF filters to common delay line circuitry for making the information, which represents contiguous range samples, contiguous in time.

United States Patent [191 Whitnah et al. May 22, 1973 15 1 HIGH-RANGERESOLUTION RADAR 3,299,427 l/1967 Kondo ..343/17.1 R REAL-TIME DISPLAYAPPARATUS 3,303,497 2/ 1967 Chubb.... ..343/7.3 3,423,754 1 1969 G t..343/17.2R [75] Inventors: Richard G. Whitnah, Bremerton, mm

Abe Goldstein! Santa Primary ExaminerMalcolm F. Hubler Cahf'Attorney-11. S. Sciascia et al. [73] Assignee: The United States ofAmerica as represented by the Secretary of the [57] ABSTRACT Navy, g m Ahigh-range resolution radar display apparatus for [22] Filed: 1 1, 1971generating a composite coarse and fine real-time radar displaysimultaneously without an intermediate PP -I 1 0,688 storage system. Onedisplay comprises an extended length display which allows an operator tosearch an [52] us. CL 343/172 R extended delta range and is generated bypeak detect- [511 Int Cl G015 9/12 ing range information from narrowbandwidth IF fil- [58] Fie'ld 343/7 3 17 IR ters. The other display is alimited extent display featuring the maximum resolution capability ofthe correlation radar system for detailed target examination and isgenerated by feeding the information from [56] References Clted each ofthe IF filters to common delay line circuitry UNITED STATES PATENTS formaking the information, which represents contiguous range samples,contiguous in time. 3,140,489 7/1964 Downie ..343/l7.2 R 3,181,1564/1965 Ward ..343/17.2 R 5 Claims, 3 Drawing Figures lF FILTER '2 AMP 28CIRCUIT L I [[0 3O N-IF XMITTER AMPS N-VlDEO i 14 16 30V PEAK SUM VIDEODETECTOR IMAGE L. O. REJECTION F'LTER DELAY LINE 2 (2O 2 SERIEiVlDEOSLOW TIMING V SWEEP 26 CIRCUIT GENERATOR 1 P Y DEVICE j l F FAST a SWEEPFROM TIMING 111 111211 A'( 11mm GENERATOR OHCUIT 115110 1 AXIS PAIENTEII3, 735.41 1

SHEET 1 [IF 2 Ho) N l I} 1 AIF I Nb) i l/Af REAL TIME VIDEO FOREFFECTIVE RANGE INTERVAL R RESOLUTIONN I I(c) I I A REAL TIME vIDE0 FORRANGE INTERvAL RN RI RN FILTER FIG. I I2 28 cIRGuIT IO 30 N-IF XM'TTERAMPS N-VIDEO Ir 3Ob PEAK SUM VIDEO DETEcToR IMAGE L. o. REJEcTloN T LINE20 22 C SERIE VIDEO sLow I 32 TIMING SWEEP 2 6 CIRCUIT GENERATOR DISPLAYDEVICE 24 g? FAST SWEEP FROM TIMING TO DISPLAY DEVICE GENERATOR CIRCUITLJ'ITJ'LTO Z-AXIS INVENTOR- ABE GOLDSTEIN FIG. 2 BY RICHARD G. WHITNAH QWYM PAIENIED 22 I915 3,735, 41 1 SHEET 2 OF 2 40-FOOT DISPLAY 5- FOOTRESOL UTION l-MILE DISPLAY 40- FOOT RESOLUTION DESIGNATION MARKER FIG. 3

INVENTOR.

ABE GOLDSTEIN BY RICHARD G. WHITNAH HIGH-RANGE RESOLUTION RADARREAL-TIME DISPLAY APPARATUS CROSS REFERENCES TO RELATED APPLICATIONSThis case is closely related to the following copending patentapplications which are hereby incorporated by reference:

a. A Passive-Active Missile-Seeker System, Ser. No. 174,576, filed onAug. 13, 1971, by Goldstein et al;

b. Digital Range Tracking Apparatus for High- Range ResolutionCorrelation Radars, Ser. No. 173,336, filed on Aug. 13, 1971, byGoldstein et al; and,

c. Automatic Gain Control Circuit for High-Range Resolution CorrelationRadar, Ser. No. 174,577, filed on Aug. 13, 1971, by Goldstein et al.

BACKGROUND OF THE INVENTION In a high resolution radar system where thevideo pulsewidth from a point source target is essentially equal to thetransmitted pulsewidth but the range resolutions cell is many timessmaller, the presentation of returns from the many targets to bedisplayed in appropriate scale and position in real-time requiresspecial consideration. Specifically, in a radar system with rangeresolution capabilities in the order of 5 feet, the quantity of datapossible for presentation to an operator is often beyond his ability tocomprehend and beyond the resolution capabilities of available displaydevices.

Also, the effective resolution length of a radar system is determined bythe RF processing bandwidth while the data rate is controlled by themechanization of the receiver filter channels. However, since the timeextent of the receiver output video is often much greater than thesystem resolution, and if a continuous display sweep is generated eachPRF, the display will appear confused to the operator. The presentsystem overcomes these difficulties by providing a specialhorizontal/vertical and blanking program to generate a composite A-scopetype of display.

SUMMARY OF THE INVENTION A high-range resolution radar real-time displayapparatus for generating a composite display is disclosed. An extendedrange display is generated in a search mode so that targets can beexamined for particular extent characteristics prior to initiation ofrange track, and a high-resolution display is generated in a track modeso that selected targets can be positioned within the actual trackinggate prior to initiation of automatic range track. The composite displayis generated by a novel horizontal/vertical and blanking program whichmakes unnecessary the use of an intermediate storage system. Informationfrom parallel receiver channels is peak-detected to provide video forthe extended range display and the high-resolution video is generated byrange gating the information at the target range and then progressivelydelaying each video sample in a common delay line and then seriallysumming the delayed samples to thereby provide a display of contiguousrange sample contiguous in time.

OBJECTS OF THE INVENTION The primary object of the present invention isto provide a high-range resolution radar real-time display apparatusfeaturing a dual-display capability.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified illustration oftypical waveforms used in the present invention.

FIG. 2 is a simplified schematic block diagram of a high-rangeresolution radar system incorporating the present real-time displayapparatus.

FIG. 3 is a simplified illustration of an exemplary real-time dual-tracedisplay.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the presentinvention shown in FIG. 2 is intended to be used primarily, but notexclusively, with a high-range resolution correlation radar system ofthe type disclosed in in the above-referenced copending patentapplication entitled A Passive- Active Missile-Seeker System. The abovereferenced patent application fully describes the high-resolution radarsystem and its operation, therefore it is only necessary to describe itherein in brief form using exemplary values. Essentially, the systemuses a transmitted linear FM waveform, as shown in FIG. 1(a), which isprocessed in a receiver to yield an active filtering form of pulsecompression. Parallel receiver processing is used to maintain data ratewhile generating an analog form of range tracking and while generatingan accurate antenna pointing angle output by means of sequential lobing(conical) error generation.

The system shown in FIG. 2 generates a radar capable of discriminatingagainst point reflectors located within a gated pulse length (-r) ofeach other. The transmitter 10 transmits ZOO-MC FM (chirp) signals bymeans of a four-quadrant, flat-plate array antenna 12. A correspondinglocal oscillator signal, as shown in FIG. 1(b), is generated by thelocal oscillator 14. The LO. signal consists of eight recurrent sweepsfor a l usec duration and has a retrace time of 0.28 usec whereby thetotal time required for eight sweeps corresponds to a range of 5l20-feet which is defined as the positionable delta range for rangelock-on.

The returned signal is correlated with the generated LO. signal in theimage rejection mixer 16 whose output is fed through an IF amplifier 18to the IF filter circuit 28 comprising N-IF narrow bandpass filters.Timing signals are provided by the timing circuit 20.

As shown in FIG. 1(a), the high resolution radar system transmits apulse of width, "r, and which is swept over the frequency spectrum Af.As shown in FIG. 1(b), the receiver local oscillator signal is offset byAIF and swept through the same Af as the transmitted spectrum in time,1', at a delayed time. As shown in FIG. 1(c), a target whose range, R inradar time is equivalent to the start of the local oscillator sweep willappear at the output of the radar mixer at the IF frequency and willhave most of its energy contained in a bandwidth l/1- centered at the IFfrequency. When detected in the filter circuit 28, the resultant videowill have a width approximately equal to r.

The effective resolution or pulsewidth is, however, equal to l lAfbecause, if the local oscillator sweep were started l/Af later, the sametarget at R would be outside of the IF passband. Conversely, if thetarget were located at a distance equal to l/AfX C/2 closer or furtherin range, and if the L.O. sweep time were constant, the same resultwould obtain. To examine the range cells l/Af between R and R the L.O.sweep must therefore be started l/Aflater each successive PRF, or aplurality (N) IF filters spaced at 1/-r through Af must be used in thefilter circuit 28.

Thus, the output of the mixer 16 is processed in at least eight parallelfilter channels in the IF filter circuit 28. Each channel providesinformation about a foot extent of range return which is the selectivelypredetermined range resolution for the radar system of FIG. 2. Sinceeach filter channel represents a 5 foot range sample per L.O. sweep, andsince eight receiver channels are used for display generation, a 40 footrange sample is generated per L.O. sweep.

Therefore since each L.O. sweep can generate only a 40 foot rangesample, there must be sixteen 1.28 X 500/40)] L.O. patterns to provide acomplete sample of the 5,120 foot (one nautical mile) extent. Howeversince it is necessary to examine the target for particular extentcharacteristics prior to initiation of range track, and since it isadvantageous to position the selected target within the actual trackinggate prior to initiation of automatic range track, the system isprovided with a dual display capability. That is, the display has twotraces. One trace comprises a 5,l20 foot extent, while the other is ahigh-range resolution display encompassing only a 40 foot range extent.A complete interpulse period is required to generate the second extentdisplay mode.

The high-range resolution information as generated by the range samplingtechnique is appropriately sorted" for presentation to the displaydevice 32 with real-time processing for system operation verification.That is, since the range is sampled at discrete intervals each PRF (at arange spacing determined by the transmitted pulse of r 1.0 usec and therecovery time of 0.28 usec for the local oscillator linear FM sweepgenerator), the sampled length is determined by the number of parallelnarrowband receiver channels employed. The effective resolution lengthof system is determined by the RF processing bandwidth for the data rateis controlled by the design of the parallel channels.

However, since the time extent of the receiver output video is muchgreater than the system resolution, and if a continuous display sweep isgenerated each PRF, the display would appear confusing to the operator.To overcome this difficulty, the system is designed to provide a specialhorizontal/vertical and blanking program to generate two displays on acommon scope as shown in FIG. 3. The lower trace comprises an extendedlength 1 mile) manually selected trace which allows an operator tosearch an extended (delta) range. This dis play has an effectiveresolution of N (where N is the number of parallel IF filter channels)times the system range resolution so that the target detectionproperties of the high resolution system can be maintained while theoperator is given an extended display for target location andidentification. A target designation marker (gate) is displayed as anegative deflection below the l-mile display video to facilitate targetselection and as described in the above-referenced copending patentapplication entitled A Passive-Active Missile-Seeker System."

The upper trace comprises a limited extent display generated duringtrack mode and featuring the maximum resolution capability of thecorrelation radar systern (e.g., 5 feet) for detailed targetexamination. In F IG. 3, the upper trace presents a 40 foot rangeinterval starting at the target designation gate, thus allowing highresolution examination of a selected target.

The 1 mile trace is generated during search mode by peak-detecting the40 foot IF range information output from each of the eight filterchannels doing eight successive L.O. sweeps and sixteen PRFs. Thedetected IF signals from the eight gaussian filters are amplified in theN-IF amplifiers 30a and ORD" in the peak detector (OR" gate) 30b toprovide peak detection of the largest 5 foot resolution return withinthe 40 foot interval examined by a given L.O. sweep.

This output is termed the sum video and is used to present the 1 mile,40 foot resolution display. The ORD" video signal from the eightchannels (assuming a target is present) will be of 1.0 usec duration.However, 1.0 usec represents 500 feet of radar range. Thus to displaythe proper target resolution at the proper range, the sum video must becompressed by a factor of 16 and must appear at the start of theassociated L.O. sweep.

It can be seen that on one PRF, a total of only eight targets may bepresented and would appear at 1.25 usec intervals. To provide returns inthe other fifteen 40 foot intervals the L.O. sweep and display timingmust be stepped nsec on each successive PRF, thereby filling in thetotal one-mile search. A trigger synchronous with the L.O. timing can beused to provide this stepping function.

The 1 mile search sweep is generated by summing a slow (11.5 usec sweepfrom the sweep generator 22 with a fast 1.0 usec) sweep from the sweepgenerator 24. The slow sweep is started in synchronization with thereceiver L.O. sweep at a delayed range R,, and the fast sweep is startedat the beginning of each L.O. sweep.

When summed, the sweeps produce at point 26 a staircase" sweep which isthen applied to the horizon tal axis of the display device (CRT) 32. The1.0 usec video pulse is caused to dwell by virtue of the horizontalsweep and appears to be 40 feet or 80 nsec wide. The horizontal sweepthen steps to the next receiver L.O. sweep position in 80 nsec, makingthe next target (if present) appear to be 640 feet further out in range,i.e., 1.25 usec.

The staircase sweep will thus cause video signals having a pulsewidthequal to 1 and which are applied to the vertical axis of the displaydevice to appear in real-time, in the proper range sequence and with apulsewidth commensurate with the effective resolution of the system. Onsuccessive PRFs the timing of the L.O. 14 is moved N/Af to cover therange of interest.

In other words, the horizontal trace appears as a staircase" voltage sothat the display trace is deflected in the vertical plane an amountproportional to received target amplitude for approximately the durationof the received energy (equal to the transmitted pulse length). As thenew range sample is generated by retriggering the linear FM sweepgenerator, the step horizontal voltage occurs to position the beam in adisplay position compatible to the next range sample. Simultaneouslywith the step horizontal voltage, a blanking pulse is applied to thedisplay Z-axis to clamp the display beam and prevent displayinginformation as the beam shifts along the horizontal axis. Bycontinuation of this process and by controlling precisely the horizontaldeflection voltage, the search video is sorted" directly onto thedisplay without the requirement for an intermediate information storageand retrieval system. In this manner a real-time display is generated.

The high resolution display is presented on the second trace every 17thPRF period and is the only trace presented in track mode at which timeit appears every PRF. The start time occurs at the same range as thetarget gate on the 1 mile display, and in operation, the range delay ismanually varied until a target of interest is positioned at the rangegate, at which time the target will appear on the upper trace. In thetrack mode, the center of the display will track a chosen target.

The high resolution display is generated as follows. The eight filterchannels of contiguous 5 foot range intervals are gated for 1.0 usec atthe target range. All of these signals (for an extended range) occursimultaneously within 80 nsec. Since the duration of each video pulse is1.0 usec, each successive 5 foot range interval must be delayed 1.0 usec(r I/Af) more than the preceding range and then summed together.

Thus range one video (-5 feet) occurs without delay and range eightvideo (35-40 feet) is delayed 7.0 usec, and the total display is 40 feetin 8.0 usec or feet/usec. The video thus delayed is simply presented(contiguous in time) using a linear sweep of more than 8.0 usec.

A single tapped delay line 300 of 7.0 usec duration is used to performthe successively increasing delay from the first to the last channel andalso performs the summing function. Impedance matching of the multipleinputs to the delay line is accomplished by the use of constant currentdrivers.

Thus it can be seen that a new and novel real-time display apparatus forhigh-range resolution correlation radars has been disclosed.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a high-range resolution correlation radar system wherein returnedsignals are correlated with local oscillator sweeps and wherein parallelreceiver processing is utilized including a plurality of IF filterchannels, real-time display apparatus comprising:

IF amplifier means connected to the output of each of said filterchannels wherein each of said filter channels provides a range sampleper local oscillator sweep corresponding to a target length equal to therange resolution of said radar system and wherein said range samplescomprise contiguous range information;

first means connected to the output of said amplifier means and beingresponsive to the contiguous range information output thereof, when saidradar system is in a search mode, to generate an extended lengthdisplay, said extended length corresponding to the total sweep time of aselectively predetermined number of sweeps of said local oscillator;

said first means including means for peak-detecting the rangeinformation output of said filter channels to produce first videosignals corresponding to the largest output thereof to be applied to thevertical axis of a display device; means for generating a slow sweep insynchronization with said local oscillator sweeps and a fast sweep atthe beginning of each local oscillator sweep;

means for summing said slow sweep and fast sweep to produce a staircasevoltage, to be applied to the horizontal axis of said display device,wherein said first video signals will be displayed in real-time;

second means connected to the output of said amplifier means and beingresponsive to the range information output thereof, when said radarsystem is in a track mode, to generate, every PRF, a high resolutiondisplay corresponding to the range resolution of said radar system timesthe number of said filter channels;

said second means including means for gating said range informationoutput at the target range to produce second video signals; and,

means for delaying said second video signals successively in aselectively predetermined manner and for summing the resulting delayedsignals to thereby produce a real-time display.

2. The apparatus of claim 1 wherein said means for peak-detecting saidrange information output comprises an OR-gate.

3. The apparatus of claim 1 wherein said display device comprises acathode-ray tube.

4. The apparatus of claim 1 wherein said means for delaying said secondvideo signals comprises a single, tapped delay line having multipleinputs.

5. The apparatus of claim 4 wherein said delay line includes constantcurrent drivers at the multiple inputs thereof for impedance matching.

1. In a high-range resolution correlation radar system wherein returnedsignals are correlated with local oscillator sweeps and wherein parallelreceiver processing is utilized including a plurality of IF filterchannels, real-time display apparatus comprising: IF amplifier meansconnected to the output of each of said filter channels wherein each ofsaid filter channels provides a range sample per local oscillator sweepcorresponding to a target length equal to the range resolution of saidradar system and wherein said range samples comprise contiguous rangeinformation; first means connected to the output of said amplifier meansand being responsive to the contiguous range information output thereof,when said radar system is in a search mode, to generate an extendedlength display, said extended length corresponding to the total sweeptime of a selectively predetermined number of sweeps of said localoscillator; said first means including means for peak-detecting therange information output of said filter channels to produce first videosignals corresponding to the largest output thereof to be applied to thevertical axis of a display device; means for generating a slow sweep insynchronization with said local oscillator sweeps and a fast sweep atthe beginning of each local oscillator sweep; means for summing saidslow sweep and fast sweep to produce a staircase voltage, to be appliedto the horizontal axis of said display device, wherein said first videosignals will be displayed in real-time; second means connected to theoutput of said amplifier means and being responsive to the rangeinformation output thereof, when said radar system is in a track mode,to generate, every PRF, a high resolution display corresponding to therange resolution of said radar system times the number of said filterchannels; said second means including means for gating said rangeinformation output at the target range to produce second video signals;and, means for delaying said second video signals successively in aselectively predetermined manner and for summing the resulting delayedsignals to thereby produce a real-timE display.
 2. The apparatus ofclaim 1 wherein said means for peak-detecting said range informationoutput comprises an ''''OR''''-gate.
 3. The apparatus of claim 1 whereinsaid display device comprises a cathode-ray tube.
 4. The apparatus ofclaim 1 wherein said means for delaying said second video signalscomprises a single, tapped delay line having multiple inputs.
 5. Theapparatus of claim 4 wherein said delay line includes constant currentdrivers at the multiple inputs thereof for impedance matching.